1. Field of the Invention
The present invention relates to a metal hollow golf club head and, more particularly, to a large-size golf club head such as a driver.
2. Description of the Related Art
As wood golf club heads such as drivers and fairway woods, hollow golf club heads made of a metal are widely used. Generally, a hollow wood golf club head includes a face portion for hitting a ball therewith, a crown portion forming the top surface portion of the golf club head, a sole portion forming the bottom surface portion of the golf club head, a side portion forming the side surface portion on the toe side, back side, and heel side of the golf club head, and a hosel portion. A shaft is inserted into the hosel portion and fixed thereto with an adhesive or the like.
Aluminum alloys, stainless steel, or titanium alloys are used as a metal for forming the hollow golf club head. Particularly, titanium alloys have been widely used in recent years.
Japanese Patent Laid-Open No. 11-216203 describes a golf club head in which the wall thickness of the sole portion is increased on the front edge side along the face portion. In FIG. 2 of this patent reference, this thick-walled portion is arranged along the overall front edge of the sole portion. In FIG. 4, the thick-walled portions are arranged on the toe and heel sides.
In order to increase the traveling distance of a shot with a metal hollow golf club head, development has been aimed at increasing the restitution of a ball by use of flexure of the face (trampoline effect). However, since the upper limit of the coefficient of restitution was set by the revision of golf rules, a demand has arisen for increasing the traveling distance by another method. Note that in a so-called high restitution golf club head which utilizes the trampoline effect, a long traveling distance can be obtained when hitting a ball at the face center. However, when the hitting point is off the face center (off-center hit), a long traveling distance cannot be obtained.
A golf club head described in Japanese Patent Laid-Open No. 11-216203 mentioned above can achieve a low center of gravity of the head while keeping the balance of the moment of inertia. In FIG. 2 of the patent reference, however, since the thick-walled portion exists in the overall front edge of the sole portion from the toe to the heel, the flexure of the face portion upon hitting a ball is suppressed as a whole, and therefore the traveling distance decreases.
In FIG. 4 of the patent reference, since the thick-walled portions are separately arranged on the sole and heel sides, the flexure of the face portion upon an off-center hit is suppressed, and therefore the traveling distance decreases. In addition, since the flexure of the face portion is large when hitting a ball at the face center, the coefficient of restitution readily exceeds the restriction defined by golf rules.